This invention relates to water treatment facilities and in particular to treatment of a stream of water containing suspended solids in which the solids are coagulated by a flocculant to encourage settling. The invention is directed to optimization of flocculant feed rates for varying process stream conditions.
Industrial waste water treatment facilities are frequently required to handle influent streams having varying characteristics. When this is the case, it is necessary to enable the treatment system to react to the change in the influent process stream. For example, in mining operations, waste water from different mine shafts can have different characteristics as to type and amount of suspended solids. The problem then is one of compensation for changes due to changing mine shafts and the resulting change of the water characteristics.
The invention is particularly applicable to water suspensions containing mineral values. In a typical situation, the influent stream containing the suspended particles is delivered to a flocculant pond where a flocculant, such as a water-soluble polyelectrolyte, is added in an amount specific to the stream coming from a particular mine shaft. The amount of flocculant is that which produces the desired settling rate. When the process stream is from a different mine shaft, invariably the concentration and chemical makeup of suspended solids is different, requiring a different feed rate for the flocculant to achieve maximum settling efficiency. In the past, compensation in the amount of flocculant feed has been by visual observation or by placing solids monitors directly in the tailings pond. The former obviously is little more than a guess at the proper feed rate, while the latter method is undesirable because the monitors are exposed to variations in eddy currents, mixing currents and other types of phenomena that affect the solids level being monitored at a single point. This type of measurement has been found to be inadequate from a total control point of view.